With the development of a gapless metal-oxide varistor lightning arrester, it has become common to locate an arrester of this type under oil within a transformer tank across the high voltage winding of a transformer to afford an enhanced voltage surge protection. Typically, the arrester is designed such that in the event of a failure, its housing will fracture for short circuit available currents, causing internal elements to be ejected. This action removes the arrester from the transformer circuit, leaving the transformer unprotected but usable in an emergency.
Since the arrester is located under oil in the transformer tank, visual or electrical evaluation is extremely difficult. Also, since the arrester is in parallel with the high voltage winding, the more common types of tests are of no value.
Known lightning arrester testers are stationary, laboratory based equipment, requiring highly skilled and technical people to operate. A method and apparatus for determining the condition of a gapless metal-oxide varistor arrester is disclosed in U.S. Pat. No. 4,803,436. However, the test procedure disclosed appears complicated, requiring skilled and technical personnel for its use, operation and interpretation of the test results. Also, the inherent current losses that a transformer exhibits at the frequency used in the Kresge apparatus are quite high. Thus, a great deal of energy must be expended to overcome these losses. This limits the range of testing capability of the Kresge apparatus. Further, the high current discharge capacitors used in the Kresge apparatus can be destructive.